A student is studying the properties of different types of electromagnetic radiation. They are comparing visible light to X-rays. Which of the following statements accurately describes a fundamental difference between these two types of radiation?
- AVisible light has a higher frequency than X-rays.
- BX-rays travel faster in a vacuum than visible light.
- CVisible light has a longer wavelength than X-rays.
- DX-rays have less energy per photon than visible light.
Show answer & explanationAnswer & explanation
Correct answer: C. Visible light has a longer wavelength than X-rays.
All electromagnetic radiation, including visible light and X-rays, travels at the speed of light in a vacuum (approximately 3 x 10^8 m/s), so option B is incorrect. Energy (E) is directly proportional to frequency (f) and inversely proportional to wavelength (λ) (E = hf = hc/λ). X-rays are on the higher energy end of the electromagnetic spectrum, meaning they have higher frequency and shorter wavelengths compared to visible light. Therefore, visible light has a longer wavelength and lower frequency and energy than X-rays. This makes option C correct.
Why the other options are wrong
- A. Incorrect. X-rays have a much higher frequency than visible light.
- B. Incorrect. All electromagnetic radiation travels at the same speed (speed of light) in a vacuum.
- D. Incorrect. X-rays have significantly higher energy per photon than visible light, which is why they are used for medical imaging (penetration).
Electromagnetic Spectrum
The electromagnetic spectrum is the range of all types of electromagnetic radiation, ordered by wavelength, frequency, and energy.
- All EM waves travel at the speed of light (c) in a vacuum.
- Energy (E) is directly proportional to frequency (f) and inversely proportional to wavelength (λ): E = hf = hc/λ.
- Spectrum order (low to high energy/frequency, high to low wavelength): Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma ray.
Memory trick: Radio's Really Low, Gamma's Got Great Guts (energy).